Various guide rail systems are known that guide containers moved by one or more conveyors. As is well known in the art, an interior portion of each container defines a volume therein. Typically, the containers are respectively moved by the conveyors when they are empty, i.e., before a product has been positioned in the interior portion of each container, to a filling station. Access to the interior portion is via an opening that is in fluid communication with the interior portion. Once the interior portion has been filled with the product to the extent desired, a closure or cap is positioned on the opening.
As is well known in the art, there is a risk that foreign particles (e.g., dust particles) in the ambient air may enter the interior portion, via the opening. The foreign particles may enter the interior portion when the product is positioned in the interior portion, or before or after the product is positioned in the container. In the prior art, some efforts have been made to impede the ingress of foreign particles into the interior portion before the product is positioned therein, or during filling. However, the prior art devices are cumbersome and tend to interfere with the movement of the containers on the conveyor.